A common method of manufacturing asphalt roofing shingles involves producing a continuous strip of granule covered asphaltic shingle strip material which is subsequently cut into individual roofing shingles. To produce the asphaltic strip material, either an organic felt, a glass fiber mat, or other suitable substrate is coated with hot, liquid asphalt, or a liquid asphalt and filler mixture. This may be accomplished by passing the substrate material through a coater containing the liquid asphalt, or the asphalt may be sprayed or otherwise applied to the substrate. The hot, tacky asphaltic strip is subsequently passed beneath one or more granule applicators or hoppers which apply the protective and/or aesthetically pleasing surface granules to the asphaltic strip material.
The manufacture of shingles from such an asphalt coated strip generally involves dispensing at least two different types of granules. "Headlap" granules, which are relatively low in cost and primarily serve the functional purpose of protecting the underlying asphalt material, are applied to a shingle at regions which will ultimately be covered by adjacent shingles when installed upon a roof. Colored granules or other "prime" granules are relatively expensive and are applied to the shingle at regions which will ultimately be visible when the shingles are installed upon a roof. Prime granules are disposed upon the asphalt strip for both the functional purpose of protecting the underlying asphalt strip and for the purpose of providing an aesthetically pleasing roof. In a typical shingle manufacturing process, the continuous asphalt coated strip may be sufficiently wide to allow for each predetermined length of the strip to be cut into several roofing shingles of such predetermined length. A traditional size for a roofing shingle is three feet by one foot. For example, some plants utilize an asphaltic strip which is sufficiently wide to allow three, one foot wide shingles of a predetermined length to be cut from each such length of asphaltic strip. However, other plants utilize an asphaltic strip which is sufficiently wide to allow four, five, or six, one foot wide shingles to be cut from each length. In the manufacturing process, the asphaltic strip is conceptually divided into an equal number of prime lanes, and headlap lanes. Prime lanes receive an application of prime granules while headlap lanes receive an application of headlap granules. In a three shingle wide configuration, the asphalt coated strip therefore is divided lengthwise into six lanes, three headlap lanes and three prime lanes. When a desired length of the asphalt coated strip is cut into three shingles, each shingle will be comprised of a length of headlap lane and the adjacent length of prime lane.
One problem commonly facing homeowners and others having asphalt shingled roofs, among other types of roofs, has been the growth of algae and fungus on the exposed surfaces of the roof. On a roof covered with asphalt shingles, this problem manifests itself as severe discoloration of the exposed shingle surfaces. Although this algae and fungus growth is especially prevalent in the Gulf Coast area of the United States and other warm and humid climates, it has also been found to occur in the northern regions of the United States. The discoloration generally becomes visibly apparent during the second or third year after the roofing shingles have been applied, beginning as dark spots which develop into dark streaks which eventually cover a majority of the roof. For aesthetic and sun reflective purposes, granules disposed upon the exposed or prime portions of roofing shingles are often white or light-colored and such fungus or algae or other microorganism growth on a light-colored or white shingle is particularly noticeable and unsightly.
To combat the problems associated with the growth of fungus, algae, and other microorganisms upon the exposed surfaces of roofing shingles, it is generally known to include, upon the exposed surfaces of the shingles, granules composed of or containing copper and/or other metals such as zinc, or particles of metallic zinc or copper. When wetted by rain or otherwise, such granules release copper and zinc compounds respectively which act as algicides and/or fungicides to inhibit the growth of algae and/or fungus. Such copper, zinc, or other metallic compound containing granules are very expensive, even when compared to ordinary prime or colored granules. They also may not be the same color as the prime granules being used. Therefore for aesthetic and economic reasons, the exposed surfaces of such algae and fungus resistant shingles contain primarily ordinary colored "prime" granules and a relatively small percentage of the expensive copper or zinc containing granules interspersed among the ordinary prime granules.
To minimize costs and to maximize algae and fungus fighting effectiveness, it is generally desirable to have a predetermined percentage of the anti-microorganism copper or zinc containing granules disposed upon the prime surface of each shingle. Such granules have heretofore been mixed with the prime granules to this predetermined percentage by weight or volume and applied with the ordinary prime granules to the prime lanes of the strip of asphalt covered material. However, because of normal variations in the manufacturing process, the weight of prime granules applied to each length of the various prime lanes of the asphalt strip can vary. This variance necessarily causes a deviation from the desired predetermined percentage of copper or zinc containing granules being disposed upon the prime areas of the asphalt strip. This results in some shingles having more copper, zinc, or other such microorganism resistant granules than is necessary while others may have an insufficient amount of such granules as is necessary to effectively fight fungus and/or algae.
In addition, the manufacture of roofing shingles necessarily involves dispensing more granules onto the asphalt coated strip than are necessary to coat the strip. This excess ensures that all areas of the strip are coated to provide a superior shingle, and prevents the hot, tacky asphalt coated strip from contacting and sticking to the rollers of a manufacturing production line. After the initial application of granules, the continuous strip of asphalt and granule coated material is passed around an apparatus for removing these excess or "backfall" granules. This apparatus is commonly a large diameter drum referred to as a slate drum. Backfall granules are collected in a backfall hopper and are reapplied to the asphalt coated strip. In the process of removing the excess prime and headlap granules, it is possible to keep the backfall headlap granules from commingling with the backfall prime granules. This is desirable because such granules can then be re-applied through the backfall hopper to the appropriate lanes of the strip of asphaltic material. It would be undesirable to apply backfall headlap granules to the prime lanes of the asphaltic coated strip. However, the process of preventing the backfall headlap granules from commingling with the backfall prime granules necessarily causes some backfall prime granules to become commingled with the backfall headlap granules. This results in some of the backfall prime granules being applied to the headlap lanes of the asphaltic strip through the backfall hopper. Such application of the relatively expensive backfall prime granules to the headlap regions of the asphaltic strip is referred to as the "downgrading to headlap" of the prime granules. This also causes some of the very expensive anti-microorganism granules which were mixed with and applied simultaneously with the ordinary prime granules to be "downgraded to headlap" where their algicidal or fungicidal properties are not needed and are not helpful.